In recent years, with the widespread use of public wide area networks such as the Internet (hereinafter referred to (hereinafter referred to as “LAN”) and along with the increased communication rate of these networks, a variety of data have been communicated by using personal computers and various types of electronic AV devices over these WANs and LANs.
This widespread use of these networks enables content data, such as video data, audio data, and program data, to be conveniently sold or shared by individuals. However, content data which is protected by copyright is sometimes illegally distributed because of such convenience. To prevent this, various types of countermeasures are proposed.
For example, some music download services limit the storage medium that stores the downloaded audio data to a storage medium having predetermined protection against being copied.
Additionally, for example, in communication of content data over a small network, such as a network based on IEEE 1394 standard, the encrypted content data are transferred after authentication to prevent the content data from being transferred to an unauthorized device.
Unfortunately, a communication scheme that prevents the illegal distribution of content data has not yet been established for IP protocols, which are commonly used for WAN communication. One possible solution is to limit the area of communication to a LAN when distributing the content data over an IP protocol. To limit the communication of content data within the LAN, it must be determined whether or not the other side communicating the content data is located on a LAN or a WAN. A method for such a determination, however, has not yet been established.